The solution to Eq. (REF ) consists of casting the bilinear form
in the standard form (REF ), using the relations between
\({\hat{T}}_l\)  and projectors (REF ), inverting the result using
(REF ) and, finally, using the inverse relations (REF ).
In principle, this procedure works for the bilinear form of the total
action (REF ) for an arbitrary model of quantum gravity if the
chosen gauge-fixing term makes the bilinear form non-degenerate.
Usually, the
Faddeev-Popov procedure is sufficient in this respect, but if the
original theory had an extra symmetry (e.g., the conformal one), one
needs to apply an additional gauge fixing, e.g., setting
\(h=h^\mu _{\,\,\mu }=0\)  [1]}.
